Methadone is widely used for the treatment of opioid dependent pregnant women, yet little is known about its effects on the developing fetus. Previous research by this group of investigators found that methadone treatment during pregnancy directly impacts fetal neurophysiology independently of maternal physiology. Maternal methadone administration was associated with significant depression in fetal neurobehaviors. This proposal seeks to: 1) Determine the effect of methadone treatment during pregnancy on maternal and fetal neurobehavioral functioning at trough and peak maternal methadone levels using single dose methadone therapy. This includes controlling for covariates such as individual maternal and fetal factors, which mediate or moderate these effects, and of factors that may potentiate the expression of neonatal abstinence syndrome. 2) Determine whether split dose methadone therapy for pregnant women lessens or ameliorates the previously observed deleterious effects of single dose treatment on maternal physiologic and fetal neurobehavioral functioning. 3) Determine the effects of buprenorphine treatment on maternal physiologic and fetal neurobehavioral functioning and compare them to those found in opioid dependent pregnant women treated with methadone. This aspect of the proposal will be in collaboration with the NIDA funded multi-site, double blind, randomized controlled study evaluating the effect of buprenoprphine versus methadone on neonatal outcome. The project will utilize a state-of-the-art computerized fetal actocardiograph and data analysis program to simultaneously evaluate fetal movement and heart rate, the interaction between the two (coupling) and maternal physiologic parameters;build upon pilot data obtained from a Mentored Clinical Scientist award received by the PI, and bring together the expertise of three established research teams. Information gained from this proposal has the potential to significantly impact the way in which we treat the difficult and high-risk population of opiate dependent pregnant women.